The present invention relates generally to an apparatus for detecting and controlling a combustion state in an internal combustion engine.
A Japanese Patent Application First Publication No. Showa 62-85148 (published on Apr. 18, 1987) exemplifies a previously proposed total engine control apparatus for an internal combustion engine.
In the above-indentified Japanese Patent Application First Publication discloses an Exhaust Gas Recirculation System (hereinafter simply referred to as EGR) rate control in which a basic EGR rate is derived from a look-up table of a basic EGR rate on the basis of an engine operating condition such as an engine revolution speed and an engine lead, a combustion interval of time is calculated on the basis of a signal derived from an inner cylinder pressure sensor installed For each engine cylinder, a correction quantity of the basic EGR rate is derived on the basis of the engine revolution speed and intake air quantity (engine operating condition) and on tile basis of an optimum combustion interval map, the correction quantity is used to correct the basic EGR rate to derive a final EGR rate, an EGR valve is operated via driving means on the basis of the final EGR rate so that a recirculation quantity of EGR is optimally controlled.
On the other hand, an air/fuel mixture ratio control apparatus is generally such that when the control for a fuel supply quantity is executed, a feedback correction coefficient is set according to a rich state or lean state of a detected air/fuel mixture ratio based on a signal output from an oxygen concentration (O.sub.2) sensor installed on an exhaust gas passage, the fuel supply quantity is corrected on the basis of the feedback correction coefficient so as to derive a final fuel supply quantity, thus the air/fuel mixture being feedback controlled to reach a stoichiometric air/fuel mixture ratio. This control of air/fuel mixture ratio causes a periodic variation in the air/fuel mixture ratio.
The above-described air/fuel mixture ratio control and EGR ratio control systems are also exemplified by Japanese Patent Application First Publications No. Showa 60-173361, No. Showa 57-41451, No. Showa 60-173361.